Power adapters or power supply apparatuses are indispensable electronic devices for many kinds of electrical apparatuses and information apparatuses. As is known in the art, several electronic components are mounted on a printed circuit board, which is accommodated in a power adapter or a power supply apparatus. When the power supply apparatus operates, these electronic components generate energy in the form of heat with higher or lower power. If the generated heat is not effectively transferred to the surrounding or dissipated by other suitable means, the excessive heat or the locally elevated temperature might result in the failure of the electronic components or the breakdown of the whole product. Furthermore, the locally elevated temperature on the external wall of the housing leads to some problems impairing safety.
For example, the printed circuit board of the power supply apparatus has mounted thereon many higher and lower power electronic components. The higher power electronic components includes, without limitation, transformers, metal-oxide-semiconductor field effect transistors (MOSFETs), bare dice, diodes, inductors or windings. The lower power electronic components includes for example capacitors or resistors. Since the higher power electronic components are disposed at very short distances between each other, a local region of the power supply apparatus has an extremely high temperature. The extremely high temperature on the external surface of the housing may burn the user or ignite articles in contact therewith, for example papers, tablecloths, etc.
Please refer to FIG. 1, which schematically illustrates a cross-section of a power supply apparatus. Within the housing 10 of the power supply apparatus, a printed circuit board 11 is disposed. Many electronic components are mounted on the printed circuit board 11. For neat drawings, however, only two electronic components 12 and 13 indicating a higher and a lower heat generation sites, respectively, are shown in the drawing. When the power supply apparatus operates, the electronic components 12 and 13 generate energy in the form of heat with higher or lower power such that a higher temperature TH and a lower temperature TL are produced thereon. When the heat generated from the electronic components 12 and 13 transfers to the housing 10 via the air layer 14, the temperatures of the regions 16 and 17 above the electronic components 12 and 13 are also higher and lower, respectively. Therefore, the region 16 has a locally elevated temperature. Such locally elevated temperature may result in safety problems, for example the user is burnt or even a fire accident occurs. The conventional method for enhancing homogenous temperature distribution is implemented by attaching a heat sink (not shown) on the top surface of the higher power electronic component 12 in order to increase the heat transfer area. However, such method fails to effectively reduce the locally elevated temperature on the external surface of the housing.